The status of live viral vaccination in early life.

The need for neonatal vaccines is supported by the high disease burden during the first year of life particularly in the first month. Two-thirds of childhood deaths are attributable to infectious diseases of which viruses represent key pathogens. Many infectious diseases have the highest incidence, severity and mortality in the first months of life, and therefore early life vaccination would provide significant protection and life savings. For some childhood viral diseases successful vaccines exist, such as against measles, mumps, rubella, varicella, influenza poliovirus, and rotavirus, but their use in the first year particularly at birth is not yet practiced. Vaccines against other key pathogens continue to elude scientists such as against respiratory syncytial virus. The obstacles for early and neonatal vaccination are complex and include host factors, such as a developing immune system and the interference of passively acquired antibodies, as well vaccine-specific issues, such as optimal route of administration, titer and dosing requirements. Importantly, additional host and infrastructure barriers also present obstacles to neonatal vaccination in the developing world where morbidity and mortality rates are highest. This review will highlight the current live viral vaccines and their use in the first year of life, focusing on efficacy and entertaining the barriers that exist. It is important to understand the successes of current vaccines and use this knowledge to determine strategies that are successful in young infants and for the development of new vaccines for use in early life.